The apparatus disclosed in Japanese Laid-open Patent Application 2010-256894 employs a system in which the developer is discharged using a bellow pump provided in the supply container. More particularly, the bellow pump is expanded to provide a pressure lower than the ambient pressure in the supply container, so that the air is taken into the supply container to fluidize the developer. In addition, the bellow pump is contracted to provide a pressure higher than the ambient pressure in the supply container, so that the developer is pushed out by the pressure difference between the inside and the outside of the supply container, thus discharging the developer. By repeating the two steps alternately, the developer is stably discharged.
In the apparatus disclosed in 2014-186138, a storage portion accommodating a constant amount of the developer is provided adjacent to the discharge opening, by which the amount of the flow of the developer into the storage portion is controlled. With this structure, more stabilized discharging property is accomplished than that of the supply container disclosed in the Japanese Laid-open Patent Application 2010-256894.
However, in the apparatus disclosed in Japanese Laid-open Patent Application 2010-256894 or 2014-186138, the use is made with a bellow pump to produce a pressure difference between the total inside volume of the supply container and outside of the supply container. Therefore, a large pressure difference is required between the inside of the developer accommodating chamber of the supply container and the outside in order to assure that the developer is sufficiently loosened and to stably discharged from the beginning, even in the case that the developer of the storage portion provided adjacent to the discharge opening inside the supply container is packed during the transportation or the like of the supply container. As a result, an expansion and contraction amount of the bellow pump is required to be large, or the inside volume of the bellow pump is required to be large. Then, the size of the supply container is large, thus requiring a large space for the supply container in the main assembly of the image forming apparatus. Under the circumstances, the structure for enhancing concentration of the air to the discharge opening during the toner discharging is desired.